1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Conducting Concentric Sphere

  1. Sep 23, 2007 #1
    1. The problem statement, all variables and given/known data

    A solid conducting sphere carrying charge q has radius a. It is inside a concentric hollow conducting sphere with inner radius b and outer radius c. The hollow sphere has not net chare. a) Derive expressions for the electric field magnitude in terms of the distance r from the center for the regions r<a, a<r<b, b<r<c, r>c.

    2. Relevant equations

    E = [1/(4*pi*epsilon_0)](q/r^2)

    3. The attempt at a solution

    I've managed to correctly answer the first two parts of the problem, however when it comes to b<r<c and r>c, I do not get the answers I should.
    Apparently, for b<r<c, E = 0 since a -q cancels the inner +q. Then, for r>c, E = [1/(4*pi*epsilon_0)](q/r^2) since the total charge enclosed is +q again.

    I think my problem lies in the fact that I don't fully comprehend what a concentric sphere is or how charge distribution on a concentric sphere works. Based on the solution, I feel I should intrepret that the neutral concentric sphere is neutral because it contain an equal number of positive and negative charges that have all collected on opposite surfaces - the negative charges on the inner surface of the concentric sphere (radius b) and the positive charges on its outer surface (radius c.) Otherwise, I don't quite understand how the -q and overall +q come into play...

    Thank you very much for taking the time to read this!
    Last edited: Sep 23, 2007
  2. jcsd
  3. Sep 24, 2007 #2


    User Avatar

    Staff: Mentor

    This might help - http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gaulaw.html

    The inner sphere has charge +q. Being a conductor, the charge resides at the surface.

    It would have a surface charge density of +q/4[itex]\pi[/itex] a2.

    This positive charge induces a corresponding -q charge on the inner surface of the hollow conductor (r=b), and consequently there is a +q charge on the outer surface r = c.

    The electric flux is based on the enclosed charge, and the +q at r=a cancels the -q charge at r=b.

    Then there is a charge +q at r=c.

    The surface density of the charge at r = b is -q / 4[itex]\pi[/itex] b2, and the surface charge density at r=c is +q / 4[itex]\pi[/itex] c2.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Conducting Concentric Sphere
  1. Concentric Spheres (Replies: 2)

  2. Conducting Sphere? (Replies: 3)